Particle-image velocimetry was employed to investigate the structure of the cold boundary layer surrounding a fire whirl generated in an experimental setup consisting of a pool fire enclosed by distant, inclined vertical vanes that deflect the entraining air. Results obtained for two different vane inclinations were compared with theoretical predictions previously derived using high-Reynolds-number asymptotics. The experiments confirmed the presence of a near-wall region characterized by pronounced inward radial flow, with its magnitude increasing with decreasing radial distance. Under the specific conditions examined, boundary-layer separation and reattachment were observed, giving rise to a long bubble of slow, recirculating flow along the wall. This feature has potential implications for future numerical modeling of fire-whirl structure and dynamics.Novelty and significanceAn accurate understanding of the flow surrounding fire whirls is necessary to support numerical investigations of their structure and dynamics. Particle-Image Velocimetry (PIV) is applied, for the first time, to obtain an experimental characterization of the cold boundary layer that develops around fire whirls. These novel measurements provide new insights into the structure and morphology of the boundary layer that are not captured by existing theories.

We investigate the dynamic characteristics corresponding to the structural fluctuations of a cantilever suspended in a turbulent flow. To investigate the intricate dynamics of the flow–structure interaction, first, we explore the ability of network analysis to identify the different dynamic states and probe the viability of using quantifiers of network topology as precursors for the onset of limit-cycle oscillations. By increasing the Reynolds number, we observe that the structural oscillations, measured using a strain gauge, transition from low-amplitude chaotic oscillations to large-amplitude periodic oscillations associated with limit-cycle oscillations. We characterize the dynamic states of the system by constructing the weighted correlation network from the time series of strain and identifying the network properties that have the potential to be used as precursors for the onset of limit-cycle oscillations. Furthermore, we use Pearson correlation to illustrate the evolution of mutual statistical influence between the structural oscillations and the flowfield. We use this information and the Granger causality to identify the causal dependence between the structural oscillations and velocity fluctuations. By identifying the causal variable during each regime, we illustrate the directional dependence through a cause–effect relationship in this flow–structure interaction as it transitions to limit-cycle oscillations.

We investigate the dynamical characteristics corresponding to the structural fluctuations of a cantilever suspended in a turbulent flow. First, we explore the ability of network analysis to identify the different dynamical states and probe the viability of using quantifiers of network topology as precursors for the onset of aeroelastic flutter. By increasing the flow rate or Reynolds number of the jet quasi-steadily, we observe that the structural oscillations, measured using a strain gauge, transition from low amplitude chaotic oscillations to periodic large amplitude oscillations associated with flutter. We characterize the dynamical states of the system for all these Reynold numbers by constructing the weighted correlation network (CN) from the time series of strain and identifying the network properties which can be used as precursors for the onset of aeroelastic flutter. Furthermore, we illustrate the evolution of mutual statistical influence between the structural oscillations and the flow field by using Pearson correlation. We use this information in conjunction with Granger causality to identify the causal dependence between the structural oscillations and velocity fluctuations. We identify the causal variable during each dynamical regime at different regions of the flow field. Therefore, we illustrate the directional dependence through a `cause-effect' relationship in this flow-structure interaction as it transitions to an aeroelastic flutter.

Face covering, commonly known as facemask, is considered to be one of the most effective Personal Protective Equipments (PPEs) to reduce transmissions of pathogens through respiratory droplets - both large drops and liquid aerosol particles. Face masks, not only inhibit the expulsion of such respiratory droplets from the user, but also protects the user from inhaling pathogen-laden potentially harmful droplets or their dried nuclei. While the efficacies of various dry face masks have been explored in the recent past, a comprehensive investigation of a wet mask is lacking. Yet, users wear masks for a long period of time and during this period, owing to respiratory droplets released through multiple respiratory events, the mask matrix becomes wet. We, herein, present an experimental study on the dynamics of sequential impacts of droplets on masks to understand how wetness affects possible penetration and secondary atomization of the impacted droplet. Two different types of masks, hydrophobic and hydrophilic, were used in this study to evaluate the underlying physical mechanism that controls the penetration in each of them.

The unsteady fluid flow past a bluff body has been widely studied, particularly due to the distinctive flow features observed in the wake of the bluff body itself. The inherently complex nature of the problem has promoted several investigations over the past few decades. Apart from the non-reacting situation, bluff bodies have also been used in reacting flows as flame holders in various practical combustors. Recently, some researchers have reported practical scenarios where a different fluid is injected from ports on the bluff body on to the free stream, and there exist a few studies on the dynamics of such a flow scenario in both the non-reacting and reacting cases. The present chapter presents a brief review of the recent developments on flow past a bluff body in the non-reacting and reacting flow situations. The chapter also highlights the distinctive dynamics of flow past a bluff body when another fluid is injected from the bluff body itself. The effectiveness of the proper orthogonal decomposition technique to analyze the dynamics of flows past bluff bodies is also highlighted.

Aerofoils have been used comprehensively in the research and development of aerodynamic equipment and machineries. Implementation of computational fluid dynamics (CFD) for study of aerofoils for numerous conditions has been on the rise. Despite the reduction in cost and efforts, the simulation data still differ considerably from the real-life data as a result of several assumptions taken in numerical simulations. Henceforth, validation against experimental data is of utmost importance. Furthermore, determination of numerical and experimental data for new aerofoil sections has been a necessity as the use of such sections may enhance the aerodynamic properties of various vehicles and instruments. In this paper, a numerical simulation has been performed to obtain the velocity profile for a non-standard aerofoil over five angles-of-attack (AoAs) including negative ones which have been validated against the data obtained from wind tunnel experimentation for conditions compatible with the simulation. The contemporary results obtained show commendable convergence.

A two-dimensional, laminar transient flow past a cylindrical bluff body, with methane injection perpendicular to the direction of the free stream flow, i.e. the cross-flow arrangement, is numerically studied. An unstructured grid finite volume method is used and simulations were carried out. The methane mass fraction and the injection velocity of methane injected from the slotted cylinder are altered simultaneously, and their effects on the combustion, flame characteristics, and fluid mechanics are investigated. The flame is anchored right in front of the cylinder and is stabilized by the wake of the bluff body. The current investigation illustrates the qualitative aspects of the vortex shedding phenomena. A particular case of injection velocity and mass fraction is studied in detail and its vortex shedding phenomena are analysed minutely. The non-reacting flow exhibits 2P mode of vortex shedding while the reacting flow exhibits the more common 2S mode. Fast Fourier transform analysis of the temporally fluctuating lift coefficient is performed for the different cases carried out in the present study.